Asistente Robótico Móvil para Misiones de Exploración y Rescate
The major goal of the ALACRANE Project is to develop new methods and techniques for mobile robotic assistants in missions of exploration, search and rescue. Particularly, the robotic assistant consists on a mobile robot equipped with a light crane and a couple of 4 DOF manipulators. The assistant will be coordinated with another mobile robot with a trailer, so that objects can be loaded and unloaded. The robot team will be lead by a human agent.
The project objectives comprise the construction of the manipulators, the development of robotic architectures for the assistants (ALACRANE Architecture) and the robot team (CROMAT-IIMa), as well as realistic experimentation with the system. Furthermore, mobile robots Auriga-I and Auriga-II, previously designed by the Research Group, will be reconfigured so as to become part of the robot team with the new multi-manipulator platform.
Asistente Robótico Móvil para Misiones de Exploración y Rescate.
CICYT DPI2005-00207
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REFERENCIA: |
DPI2005-00207 |
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TITULO: |
ASISTENTE ROBÓTICO MÓVIL PARA MISIONES DE EXPLORACIÓN Y RESCATE |
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INVESTIGADOR PRINCIPAL: |
ALFONSO JOSE GARCIA CEREZO |
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ORGANISMO: |
UNIVERSIDAD DE MALAGA |
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CENTRO: |
DPTO. DE INGENIERIA DE SISTEMAS Y AUTOMATICA.
E.T.S. DE INGENIEROS INDUSTRIALES. |
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DIRECCION: |
PLAZA DE EL EJIDO S/N, C.P. 29013, MALAGA |
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TELEFONO: |
+34 95 2132775 |
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E-MAIL: |
gcerezo@ctima.uma.es |
The Mechatronic System of Alacrane
A. Mechanical Design.
The ALACRANE robot is depicted in Fig. 1. This is a fully hydraulic robot that has been developed from a modified small demolition machine by Brokk®. Originally, this is an open-loop remote-controlled device. The vehicle has two motorized outriggers to provide stability when lifting or manipulating weights.
The robot consists of three main parts: the mobile base, the main arm, and the LR-Arms dual manipulator.
1) The Mobile Base: Its goal of the mobile base is to provide traction on rough terrain, such as rubble and moderate slopes. Tracked skid-steer traction is controlled by the speeds of two independent hydraulic motors (VL and VR) with encoders for dead-reckoning. The rubber belts are 130mm wide, with a longitudinal contact surface of 735mm and a distance between belt centerlines of 470mm. The performances of the robot base are related in Table 1. A power cable socket provides tethered three-phase AC power supply. Besides, for greater autonomy, a petrol-fed generator can be carried on a passive trailer towed by the mobile platform with a king-pin hitch.
2) The Main Arm: It has 5 DOF with 5 hydraulic cylinders. This redundant configuration increases its reachability of the end-effector. Characteristics of the main arm are summarized in Table II. Its payload is 120kg when it is fully extended, and 450kg in the vicinity of the arm base. These load capabilities require the outriggered vehicle.
3) The LR-Arms: A specific hydraulic end-effector that reproduces some human handling capabilities has been fully developed for ALACRANE. It consists on a dual manipulator configured as left and right Arms (LR-Arms). Its characteristics are summarized in Table III. It has 7 DOF: it adds an additional DOF to the main arm (q6), and 3 DOF for each manipulator (qL7 to qL9 and qR7 to qR9, for the left and right arms, respectively) as shown in Fig. 2. A force/torque sensor is included in the LR-Arms common base, and two 6 DOF force sensors. Both arms can be equipped with different end effectors. Besides, the stainless steel manipulator has been designed so that it can also be used as a large scale two-finger hand to grip greater size objects. Moreover, the LR-Arms tool is removable so that other standard tools can be connected to the main arm (e.g., on-off grippers, buckets or clamshell buckets, and grapples with an additional DOF).
TABLE I. ALACRANE CHARACTERISTICS
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Weight (no effector) |
380 kg |
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Width |
600 mm |
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Height |
940 mm |
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Length |
1200 mm |
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Speed, max |
1.5 km/h |
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Slope angle, max |
30º |
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Motor power |
4
kW |
TABLE II.
MAIN
ARM CHARACTERISTICS
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Range |
2400 mm |
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Base angle |
±123º |
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Slewing speed |
6,5 sec / 246º |
TABLE III. LR-ARMS CHARACTERISTICS
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Range |
1000 mm |
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Base angle |
±90º |
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Shoulder angle |
+100ºL, -100ºR |
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Slewing speed |
2,6 sec / 100º |
B. Electronic
Systems
The ALACRANE Electronic System
is based on 3 onboard PC computers connected by Ethernet and a remote base. The
low level control is assigned to a PXI PC computer (PC1). The 12 joint absolute
encoders as well as the control valves for the hydraulic actuators are connected
to PC1 through a CANopen bus. An Inertial Measurement Unit and a differential
GPS system are also read by PC1. This low level control also supports the
manual control joystick for the mobile platform and arms, and some low level
functions of the navigation controller.
The other PCs (PC2 and PC3) are Compact
PCs based on an Intel Core Duo microprocessor. PC2 supports the functional
architecture of ALACRANE and the communication level with the Remote base. PC3
supports the high level perception system: A 2D Scanner Laser –with an
additional DOF–, and two sets of video cameras.
C.
Perception
The
Mobile Base and the optional generator trailer are equipped with CCD cameras for
navigation. The one on the base is coupled to a 3D laser scanner. Another set is
mounted on the common axis of the LR-Arms. It consists of a thermal and a CCD
camera, whose images are fused for target detection and teleoperation.
The 3D scanner
device has been constructed by adding an extra degree of freedom to a commercial
2D SICK-LMS 291 time-of-flight range finder. Maximum specification values for
this sensor are: field of view 180º, horizontal angular resolution 0.5º, and up
to 80m range, ±4cm range error, 26 ms of scan time.
The 2D sensor has
been mounted into a mechanical articulation so that 3D readings are provided
directly in spherical coordinates. It incorporates a special counterweight to
reduce the required driving torque. The vertical angular resolution is 1/3º with
60º of field of view. A complete scan with 361 x 181 point is obtained in an
interval of 12 sec. The 2D rangefinder is continually sending range data with a
refresh rate faster than drive control. Synchronization is achieved by waiting
for the step acknowledgement from drive controller. At that time, the next
complete 2D scan is recorded through the serial interface and, then, a new
motion pulse is issued.